1. Field of the Invention
The present invention relates to a fuel cell suitable for a direct fuel cell. 2. Description of the Related Art
In a solid polymer fuel cell (PEM) using hydrogen as fuel or a direct methanol fuel cell (DMFC), a plurality of cells are stacked one another. Each cell is configured such that a membrane electrode assembly (MEA) is sandwiched by an anode channel plate and a cathode channel plate. In the membrane electrode assembly, an anode catalytic layer and an anode gas diffusion layer are formed at the anode side of the solid polymer proton conduction membrane and a cathode catalytic layer and a cathode gas diffusion layer are formed at the cathode of the solid polymer proton conduction membrane. In the direct methanol fuel cell, a mixed solution of water and methanol is supplied to the anode and an air is supplied to the cathode.
In the anode of the direct methanol fuel cell, the reaction is caused as follow.CH3OH+H2O→CO2+6H++6e−  (1)As apparent from equation (1), CO2 is generated in the anode. In the cathode of the direct methanol fuel cell, the reaction is caused as follows.3/2O2+6H++6e−→3H2O   (2)As apparent from equation (2), H2O is generated in the cathode.
The mixed solution made of CO2, H2O and methanol not reacted in the anode is converted into a gas/liquid phase flow and then, discharged from the anode. The gas/liquid phase flow, discharged from the anode, is supplied into a gas/liquid separator disposed at the flow path in the side of the outlet of the anode, and then, separated into the corresponding gas and liquid. The separated liquid is circulated to a mixing tank and the like via a recovering path, and the separated gas is discharged to air (refer to Reference 1).
[Reference 1] U.S. Pat. No. 6,924,055
In the anode of the fuel cell using hydrogen as fuel, the reaction is caused as follows.H2→2H++2e−  (3)
In the cases that the mixed solution of water and methanol is supplied to the anode in the direct methanol fuel cell and the hydrogen is supplied to the anode in the fuel cell using hydrogen as fuel, it is required air is supplied to the cathode sufficiently enough to cause the electric power generation in accordance to the equations (1) to (3). As of now, in this point of view, air is supplied by means of pump. In this case, however, there are shown some problems that the pump is required to be enlarged, generates noise and increases the electric power consumption.
Alternatively, the membrane electrode assembly is dried when air is supplied so that the humidity condition of the membrane electrode is changed so as to unstablize the performance of the electric power generation.